Synthesis of N,S co-doped carbon dots for fluorescence turn-on detection of Fe2+ and Al3+ in a wide pH range

N,S co-doped carbon dots (N/S-CDs) was synthesized by using β-cyclodextrin as carbon source and Reactive Black 5 as nitrogen and sulfur source. The structure of the N/S-CDs was characterized and its performance for detection of Fe2+ and Al3+ was evaluated. Experimental results demonstrated that the N/S-CDs had good stability in 10 mmol/L brine and in a wide pH range of 3–12. The N/S-CDs exhibited high selectivity for detection of Fe2+ and Al3+ by dual-modal fluorescence enhancement and visualization with the naked eye over a wide pH range. The N/S-CDs displayed good anti-interference performance and low detection limits of 6.99 nmol/L for Fe2+ and 5.5 nmol/L for Al3+. The N/S-CDs responded to Al3+ rapidly within 3 min. Measurements on particle size, zeta potential, and UV–vis and FT-IR spectra suggested that Fe2+ enhanced fluorescence of the N/S-CDs by chelating while Al3+ promoted aggregation through combination with the N/S-CDs which responded to Al3+ by aggregation-induced enhancement of emission (AIEE) mechanism.